Many individuals, particularly the elderly, suffer from deposits which clog their arteries, more commonly referred to as atherosclerosis. Quite frequently, these deposits block or restrict the flow of blood in the arteries of the lower extremeties, which limits the flow of blood to the patient's leg and foot. Lack of blood flow and oxygen to the leg and foot may be debilitating or life-threatening to the individual, and corrective measures must be taken.
Although some individuals may be treated with medication, in most cases surgery is required. Some arterial deposits may be removed or the arteries dialated with various surgical techniques, but these procedures do not work for every patient for very long. The condition may recur, requiring further action.
One procedure which has proven effective in combating atherosclerosis is to bypass the blocked artery with another blood carrying conduit. Experimentation has lead many surgeons to use synthetic type materials for replacement arteries. Such materials include an artificial tube made from Dacron or plastic. Although temporarily suitable, these artificial conduits have a tendency to become clogged once again, and therefore their use has been restricted especially in distal by-passes.
The preferred material for an arterial bypass is one of the individual's own veins. More particularly, when the femoral artery in the leg becomes blocked, it is desirable to use the greater long saphenous vein to bypass the blocked artery.
There are two ways in which a surgeon may use the individual's own vein. The vein may be harvested from the patient's leg, removed from the patient's body, and turned end for end before resetting the vein back into the body to be used to bypass the blocked artery. Turning the vein end for end ensures that the valves are oriented in the proper direction to allow the flow of blood from the heart to the leg and foot. Although this procedure is commonly used, it interfers with the integrity of the vein and long segments of small diameter veins may become blocked in the short or long term.
A second and preferred procedure is an in-situ saphenous vein bypass. During this procedure, the vein is left in place in the patient's leg, while portions of the vein are connected to the femoral artery in such a manner as to bypass the blocked portion of the artery. If the procedure were to stop here, however, the valves in the vein would prevent the flow of blood down to the leg. Therefore, an instrument called a valvulotome has been developed which is inserted into the vein to lyse or rupture and render incompetent the valves in the bypass vein.
There are two or three valvulotome instruments available today. Each is quite similar in that it includes a small cutting blade mounted on a thin stainless steel wire. To use the instrument, the surgeon makes an incision and inserts the blade into the patient's vein. The instrument is advanced into the vein past the valve which is the farthest from the incision. When the blade of the valvulotome has been pushed past the farthest valve, the surgeon then begins pulling back on the wire forcing the blade to engage with the valve cusps thereby perforating the valve and rendering it inoperative.
The blades currently in use are of several shapes. One shape is a "J" or "hook-shaped" blade which has a cutting edge on the inside of the curved portion of the hook. Another popular shape is an inverted "U" or "mushroom-shaped" blade. Other shapes are also available but all are restricted in that they have only one cutting edge. Several serious complications have arisen however with the use of these types of blades. Most problematic has been that although the blade is designed to engage with and perforate the valve cusps, it also frequently engages with and perforates the walls of the vein as the blade is pulled back through the vein. Since the vein has a tremendous number of branches, there is also the danger that the blade may snag and engage with the opening leading to these branches, and lyse this junction. When this occurs, remedial surgery must be performed to correct the inadvertent and unwanted rupture.
A further problem arises in that the existing blades do not always satisfactorily lyse the valves to allow for a sufficient amount of blood to the leg and foot. Valve cusps are "cup" shaped and are hingeably attached to the vein's inner wall. When the cusps close, they contact one another and the backward flow of blood pushes these cusps securely against one another, preventing any further backward flow. Since current valvulotome blades have only one cutting edge, the value cusps may not be sufficiently disabled, or only one cusp may be disabled at one time in the case of the "J" blade.
An additional problem with the current blade designs is that the blade is of one size while the vein itself is tapered having a larger diameter near the groin area and becomes narrower near the ankle. This causes further complications in trying to perforate valve cusps without causing trauma to the inner wall of the vein. In addition, since the blade is not retractable, it cannot be pulled back once inserted into the vein without engaging with the valves or other portions of the vein.